1. Field of the Invention
The present invention relates to the combustor of a gas turbine engine, and, more particularly, to a system for actively controlling pressure pulses in a gas turbine engine combustor in which a cancellation pulse is produced by periodically extracting air from the combustor to offset a predominant pressure pulse.
2. Description of Related Art
It is well known in the art for pressure pulses to be generated in combustors of gas turbine engines as a consequence of normal functioning, such pressure pulses being dependent on fuel-air stoichiometry, total mass flow, and other factors. Pressure pulses can have adverse effects on an engine, including mechanical and thermal fatigue to combustor hardware. The problem of pressure pulses has been found to be of even greater concern in low emissions combustors since a much higher content of air is introduced to the fuel-air mixers in such designs.
Several attempts have been made to eliminate, prevent, or diminish the acoustic pressures produced by such pressure pulses in gas turbine engine combustors. One method has been to elevate flame temperatures, which has achieved moderate success. However, elevating flame temperature is clearly contrary to the goals of low emissions in modern combustors since a relatively low temperature band is preferred. Moreover, it has been found that elevating the flame temperature in a combustor has an undesirable effect on the liners thereof.
Another proposed system has been to utilize an asymmetric compressor discharge pressure bleed. In this system, it is believed that pressure pulses in the combustor take the form of a circumferential pulse located adjacent to the combustion chamber. However, it has been found that pressure pulses within the combustor travel not only in a circumferential manner, but also in an axial manner. More specifically, pulses originating in the combustion chamber travel therein and then are reflected back through the fuel-air mixers into the cold section of the combustor. Therefore, the asymmetric compressor discharge pressure bleed has been found to be unsuccessful in effectively combating pressure pulses in the combustor.
Still another method of counteracting pressure pulses within a gas turbine engine combustor has been the use of detuning tubes positioned at the upstream side of the combustor. These detuning tubes extend into the combustor by a predetermined amount and are effective at balancing out pressure pulses having a fixed amplitude and frequency. Nevertheless, it has been found that pressure pulses within a combustor are variable with changing amplitudes and frequencies. Thus, the aforementioned detuning tubes have met with only a moderate degree of success.
Therefore, it would be desirable for an active system to be developed that effectively offsets the dynamic pressure pulses in a gas turbine engine combustor and not only is able to adapt to pressure pulses of varying amplitude and frequency, but also does not have any adverse effect on the emissions of the combustor.